Preparation And Characterization Of Inorganic Modified Seperators For Lithium Ion Battery By Electrospinning

As an important component of lithium ion battery, separator at present mainly adoptsCelgard PP membranes, but it greatly restricts the improvement of the performance of thebattery by characteristics of itself. Nanofiber membrane prepared by an electrospinningmethod has great potential in lithium ion battery due to its high porosity and ionicconductivity. As a common material for electrospun seperator, Poly （vinylidenefluoride）（PVDF） has good chemical and electrochemical stability, as well as excellent wettability fororganic electrolyte. However, without strong bonding between fibers, electrospun PVDFmembrane has poor mechanical strength which can’t meet the requirements for assembly ofbatteries, so its application has been limited to a great extent.This article explores the influence of the solvent, solution concentration, spinningvoltage on electrospun PVDF membrane and verifies the feasibility of electrospinningPVDF, the most appropriate electrospinning process conditions are DMAc/acetone=（3:7wt/wt）, PVDF solution concentration7wt%, spinning voltage20kV. But the mechanicalproperties of electrospinning PVDF membranes is not ideal which greatly limit theirapplication. Therefore, adding inorganic components for modification of membranes isselected. The prepared PVDF/SiO₂composite membranes electrospinning PVDF solutionand SiO₂sol mixture directly not only have high porosity and absorption for organicelectrolyte, but also have excellent thermal stability which greatly improves the safety ofthe battery. Compared with the Celgard PP membrane, the ionic conductivity of （9:1）composite membrane is as high as7.47×10^-3S cm^-1, and interfacial resistance between theelectrode and composite membrane is smaller than that of Celgard PP membrane. Theassembled cells adopting the prepared （9:1） composite membrane as separator have highercharge and discharge stability, higher discharge specific capacity as high as159mAh/g,excellent rate discharge performance and cycle performance with capacity retention closingto100%after50cycles.To further improve mechanical properties of composite membranes on the basis ofPVDF/SiO₂composite membranes and to improve their practical applications, we usethermoplastic polyurethane （TPU） to enhance and toughen PVDF/SiO₂compositemembranes to prepare PVDF/SiO₂/TPU three component composite membranessuccessfully. Test results show that the fiber morphologies are more neat, porosity and absorption for electrolyte get better maintainence, and the mechanical properties ofcomposite membranes are improved obviously with the tensile strength increased by43%,the elongation at break increased by261%. The results of battery tests show that theassembly batteries using modified composite membranes with TPU as separator suggestless battery polarization inside than before, and have higher discharge specific capacity andexcellent charge-discharge cycle performance. Accordingly, they prove promisingcandidates for separators of high performance lithium ion battery.